High quality lubricating oils are critical for the operation of modern machinery and motor vehicles. However, current crude oil supplies are inadequate to meet present demands for such lubricants. Therefore, it is necessary to upgrade crude oil fractions otherwise unsuitable for lubricant manufacture. As an example, high-quality lubricating oils must often be produced from waxy feeds. Numerous processes have been proposed for producing lubricating base oils by upgrading ordinary and low quality feedstocks.
Hydrocarbon feedstocks may be catalytically dewaxed by hydrocracking or hydroisomerization. Hydrocracking generally leads to a loss in yield due to the production of lower molecular weight hydrocarbons, such as middle distillates and even lighter C4-products, whereas hydroisomerization generally provides higher yields by minimizing cracking.
U.S. Pat. No. 7,384,538 to Miller discloses hydroisomerization of waxy feed for base oil production in an isomerization zone comprising a catalyst bed having at least two isomerization catalysts, wherein a first catalyst has a channel diameter of at least 6.2 A, and a second catalyst has a channel diameter not more than 5.8 A. U.S. Publication No. 20080083657 (Zones et al.) discloses dewaxing a hydrocarbon feed with a metal-modified small crystallite MTT framework molecular sieve. U.S. Publication No. 20090166252 (Daage et al.) discloses lube basestock production using two isomerization catalysts, wherein a first catalyst has a Constraint Index (CI) of not more than 2, and a second catalyst has a CI greater than 2.
Apart from product yield, another important factor in the catalytic production of base oil is the minimization of catalyst aging. In this regard, U.S. Pat. No. 5,951,848 discloses the use of a two catalyst system comprising a hydrotreating catalyst and a dewaxing catalyst. The aging of the dewaxing catalyst may be slowed by the presence of the hydrotreating catalyst layer.
U.S. Pat. Nos. 6,468,417 and 6,468,418, both to Biscardi et al., disclose the production of lube oil having a reduced tendency to form a haze by a process including contacting a dewaxed lube stock or base oil feed with a solid sorbent to produce a dehazed base oil having a reduced cloud point relative to that of the dewaxed lube stock or base oil feed.
There is a continuing need for improved dewaxing processes and catalyst systems showing increased isomerization selectivity and conversion of waxy hydrocarbon feedstocks for the production of valuable Group II and Group III base oils.